Perioperative Monitors: More Than Meets the Eye
Monitoring cardiorespiratory function, acid-base balance, and fluid therapy can be fraught with inaccurate and irreconcilable information. This statement is particularly true when using minimally invasive or non-invasive monitors that only provide digitally displayed numerical readouts of physiologic parameters. Although most monitors that digitally display one or more rates, times, pressures and percent values have become commonplace their accuracy is dependent upon one or more assumptions which must met in order for the data to be precise. Monitors that provide scalable analog or digitally derived physiologic waveforms in addition to numerical outputs are preferred to those that only provide numerical values. Changes in displayed waveforms frequently become apparent before any significant change in a digitally displayed numerical values for the same parameter. Changes in the electrocardiographic waveform often signal the development of changes in heart rate and rhythm and the development of cardiac arrhythmias. For example, prolongation of the PR interval or depression or elevation of the ST segment frequently become apparent long before there is a change in the digitally displayed heart rate or the development of a cardiac arrhythmia. Similarly, identification of changes or disturbances in the end-tidal (ET) carbon dioxide (ETCO2) waveform are almost always apparent before changes there is a change in the digitally displayed respiratory rate or end-tidal CO2 value. These examples and others will be used and extended to emphasize the importance of signal identification in conjunction with scalable numerical values in order to make informed decisions of the animal's physical status.